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OSPF Questions 2

July 28th, 2017 in ROUTE 300-101 Go to comments

Question 1

Explanation

Exstart: Once the DR and BDR are elected, the actual process of exchanging link state information can start between the routers and their DR and BDR. In this state, the routers and their DR and BDR establish a master-slave relationship and choose the initial sequence number for adjacency formation. The router with the higher router ID becomes the master and starts the exchange, and as such, is the only router that can increment the sequence number. Note that one would logically conclude that the DR/BDR with the highest router ID will become the master during this process of master-slave relation.

Reference: http://www.cisco.com/c/en/us/support/docs/ip/open-shortest-path-first-ospf/13685-13.html

Question 2

Question 3

Question 4


Question 5

Explanation

+ Standard areas can contain LSAs of type 1, 2, 3, 4, and 5, and may contain an ASBR. The backbone is considered a standard area.
+ Stub areas can contain type 1, 2, and 3 LSAs. A default route is substituted for external routes.
+ Totally stubby areas can only contain type 1 and 2 LSAs, and a single type 3 LSA. The type 3 LSA describes a default route, substituted for all external and inter-area routes.
+ Not-so-stubby areas implement stub or totally stubby functionality yet contain an ASBR. Type 7 LSAs generated by the ASBR are converted to type 5 by ABRs to be flooded to the rest of the OSPF domain.

Reference: http://packetlife.net/blog/2008/jun/24/ospf-area-types/

Question 6

Explanation

NSSA External LSA (Type 7) – Generated by an ASBR inside a Not So Stubby Area (NSSA) to describe routes redistributed into the NSSA. LSA 7 is translated into LSA 5 as it leaves the NSSA. These routes appear as N1 or N2 in the routing table inside the NSSA. Much like LSA 5, N2 is a static cost while N1 is a cumulative cost that includes the cost upto the ASBR.

OSPF_LSAs_Types_7.jpg

Question 7

Explanation

OSPFv3 uses the well-known IPv6 multicast addresses, FF02::5 to communicate with neighbors.

Note: All other routers (non DR and non BDR) establish adjacency with the DR and the BDR and use the IPv6 multicast address FF02::6 to send LSA updates to the DR and BDR.

Question 8

Explanation

NSSA External LSA (Type 7) – Generated by an ASBR inside a Not So Stubby Area (NSSA) to describe routes redistributed into the NSSA. LSA 7 is translated into LSA 5 as it leaves the NSSA. These routes appear as N1 or N2 in the routing table inside the NSSA. Much like LSA 5, N2 is a static cost while N1 is a cumulative cost that includes the cost upto the ASBR.

OSPF_LSAs_Types_7.jpg

Question 9

Question 10

Comments
  1. Anonymous
    August 5th, 2017

    Hi!

    Can you please confirm the answer to question 1, i think its B (Loading)

    https://www.cisco.com/c/en/us/support/docs/ip/open-shortest-path-first-ospf/13685-13.html

    Loading

    In this state, the actual exchange of link state information occurs. Based on the information provided by the DBDs, routers send link-state request packets. The neighbor then provides the requested link-state information in link-state update packets.

  2. Sq
    August 6th, 2017

    Question 3

    Refer to the exhibit. A network engineer executes the show ipv6 ospf database command and is presented with the output that is shown. Which flooding scope is referenced in the link-state type?
    (Exhibit missing)

    A. link-local
    B. area
    C. AS (OSPF domain)
    D. reserved

    The exibit is showing:

    Link (Type-8) Link states (Area 0)

    As its type 8 shouldn’t it be the link-local flooding scope ?

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